This invention relates to a method for controlling the zebra mussel. The invention more particularly concerns the eradication of the zebra mussel in aqueous environments including water intakes, conduits and storage systems of power and water treatment plants, and processing streams and systems of industrial plants.
The zebra mussel (Dreissena polymorpha), endemic to the Black and Caspian Seas, is unique among mollusks because it thrives only in fresh water bodies; reproduces at an astonishing rate (research suggests the female can produce more than 1 million eggs yearly); is inedible by humans; has a microscopic larval stage (veliger) that is carried, often undetected, by water currents and human activities to a multitude of environments; can survive out of water for extended periods (estimated as up to 14 days); has a relatively long life span (about five years); has sticky, hair-like threads (bysusses) which enable the mussels (both veligers and adults) to attach tenaciously to virtually any hard surface; and has a voracious appetite for microscopic plants and animals.
Since its discovery in June 1988 in Lake St. Clair, Mich., the zebra mussel has spread to all of the Great Lakes and to many inland rivers of the eastern and midwestern United States, including the Mississippi, Hudson, Ohio and Susquehanna rivers. The mussel has caused an estimated $100 million in damage to date in the United States and Canada. The damage is to inlet water systems of power and water treatment plants, to water filtration systems and conduits of industrial plants, and to boats and marine engines and pumps, caused by incrustation of the mussels on inlet and conduit surfaces. The biofouling results in severe restriction and even interruption of flow, thus affecting municipal and power plant water supplies, and industrial processes dependent on water intake from fresh water bodies.
The mussels have seriously affected the ecological balance in fresh water bodies by destroying crayfish and other humanly edible shellfish, by creating barriers in the spawning grounds of game fish, and by filtering out microscopic plants and animals that serve as food for other marine life.
It is estimated that zebra mussels concentrate contaminants about 100 times more than do fish. Thus, predators of the mussels, such as diving ducks and certain fish, can be expected to be exposed to high contaminant concentrations.
These and other threats to water use posed by zebra mussel infestations have motivated a variety of approaches to control. In addition to mechanical removal of incrustations on a periodic basis and redesign of water inlets to reduce ideal conditions for infestation, thermal backflushing and chemicals have been used. In thermal backflushing, heated discharge water in a power plant is re-directed to cool water intakes to kill the zebra mussels. The treatment has the disadvantage of sometimes resulting in fish kills.
The chemical treatments reported to date have been non-selective, too toxic for use in many waterways, too corrosive, or lacking in reasonable handling safety and/or cost. For example, although effective, chlorine treatment is accompanied by formation of toxic byproducts such as trihalomethanes and therefore cannot be used where there may be human exposure. When halides are used, it is often necessary to de-toxify streams before end use, thus adding significantly to treatment cost.
Other oxidants, such as ozone and/or hydrogen peroxide, are environmentally safe but pose safety and handling problems (ozone) or are not sufficiently active to be cost effective (hydrogen peroxide).